let it flow (head question)

[71SATELITE]

How much better will well prepped(port polish) 302 heads flow over a set of stock 71 heads on a stock 318? What would the horse power gains be using with a TQ and eddy performer intake? Thanks.

[DartGT66]

To really wake those heads up, you should have 1.88/1.60 valves installed and the bowls opened up. I can't give an estimation about the power increase, but it will propably be significant. They do not necessarily flow very much better than the old heads, but they just plain are more efficient. My only experience of the "high swirls" is of the 360 '308' heads. I had a set of 2.02/1.60 J-heads that were mildly pocket ported, and I wanted to run unleaded gas. So I bought new high swirls and installed them untouched out of the box. When I first saw them I was a little disapointed because of the smallish ports and big pushrod plunge in the intake port. Never the less, I put them on and in the first test drive the car seemed to run way better than before. And the first time at the track proved that feeling right, my best with the old heads and 3.23 gears + 205 stock tires was 14.02/100 mph, and with the high swirls the ca run 13.26/107 mph.

[71SATELITE]

Nice, thanks for the reply. It looks like I am off to the bone yard this weekend to find some 302's. Can I use my old push rods or will I have to take the ones from the donor motor? Thanks again.

[DartGT66]

The stock pushrods and rockers should work just fine. check the heads carefully, have heard they have a tendency to crack in the valve seat area, mainly between the intake & exhaust valves. i think you will happy with that swap; the smaller chamber will also pump up your compression ratio slightly.

[dwc43]

I answered on your other post. I'd find some x or j heads with the 2.02 - 1.60 valves and mill them .035" to raise compression even more than the other heads would. Do not port them. For what you wanted on the other post I think you will loose more than you gain.

[71SATELITE]

dcw you think I would loose power by porting the heads? I know you have ton of more experience so please tell me why? I have never heard this but that is why I like this website because you always learn something. Thanks for the reply and let me know.

[FASTDARTCHESTER]

71,

Built a 318 last summer with '302 heads and 1.88/1.60 valves, ported and polished. The '302's lend themselves well to creating a nice short turn radius on the exhaust port (thru porting) because when you add the bigger valve, there is more meat to create a radius (even stock the short turn is better than a standard 318 head). Exhaust port on these heads is raised compared to standard 318 head which also adds performance potential. I believe intake port is unchanged except for pushrod hole pinch...

Picked my heads up from the boneyard for 30 bucks/set. Had 'em magnafluxed and checked out by my shop and it was off to the races. I milled em 0.060" and had to get custom pushrods.

The engine is really a screamer. Haven't dynoed it or got it to the track but I will in the spring and let you know were it is.

Also have a couple more sets of '302's that I plan on sectioning this winter because I want to find out the true potential of this head. Maybe I will flow a set next summer.

I have pix, if you want them.

TD

[dwc43]

Like someone else said the 318 looses a lot low end torque if over cammed. Staying with the smaller and split duration cam I think will give you more of a gain and I think you'll lose some bottom end on the porting 'cause you want be running it in an rpm range to use it according to what you will be using it for. You could save the money and use it on something better I think.

[71SATELITE]

Chester I would love to see those pics send to 71satelite . DWC I wasn't meaning an all out port job. Just some bowl blending and a intake to head gasket match, and a little combustion chamber work. No radical changes just more efficient. You don't think that will hurt performance? I still do not understand how a port job would hurt performance? Would it cause over fueling, or a serious bog? Let me know, I am sure others would like to hear some of your experience, and going beyond stock is still pretty new to me! Thanks for the reply's guys, Chester don't forget the pics, I can't wait to see them.

[dwc43]

An engine can only move so much air. If you opened up the intake too much you loose air velocity. Carb no longer gets a good vacuum signal from the engine. The valves your choke point anyway.So the cam makes a diffrence.Running a small cam with big runners would defeat the purpose of the big runners. Gasket match wont hurt it or around the bowls. I guess I had an all out gouge the runners out port job in mind when I said that.

[ajmopar]

It's all about velocity. If the hole is too big, the air/fuel mixture becomes lazy, turbulent and the fuel droplets shear out of suspension. Another problem is that the easier the mix flows in, the easier it reverses out of the cylinder, causing poor cylinder filling, erratic mixture control low manifold vacuum and low power out put at low rpms. Everything's a trade off, and in this case a port sized for low to mid rpms is a restriction at high rpms (although the area under the curve makes up for some lack of top end power through proper gearing), and a port designed for upper rpms is a mess at low speeds. Timing advance makes up for some of the low rpm inefficiencies, but not enought to make it practical for regular daily drivers. This is why smaller headers with long primaries, smaller carbs and dual plane intakes work better on the street. They all keep the velocity up at the speed you use the engine at most with street friendly gearing. Actually the way dual plane intakes work is a whole other topic.

[dwc43]

Thanks aj. You said it much better than I did. Work nights and just got up so I have not cleared the cob webs from my head yet.

[FASTDARTCHESTER]

end of the day for me, i got the cobwebs too

[71SATELITE]

Thaks AJ the big light bulb came on, much like the venturi effect of a carb. You mentioned it so how does a duel plane work? While your at it how about spread bore?

[6 packin]

I have a little experince with the swirl heads. I think for the most part not much could be had with the port work to them. maybe 10-15 horses! For all out horse power you need some well preped 360 heads or Edelbrock heads. The swirl head does its job providing better mid range (usable power) and better fuel economy by the swirl better fuel atomization and so on. But still a bottle neck for some good high revin power. On a mild or stock engine...........sure....... but a hot street/strip you need some deep breathing heads. Even then port and polish will not help that much. Unless a hot race/strip engine would benifit most. Although this my opinion and has been provem to me over the years of weekend warrior tire blasting bonzi$#@@! blasts!

Hope i could help!

[Fast One]

I think the thing to remember is it's a factory head & not a race head, we hear about the 302 head a fair bit & expectations can be high, though when saying that it's not a put down, on the 318 engine the 302 is a good swap, being a swirl technology head there's a definite advantage using it, the swirl & tumble are used to improve octane tolerance by making a quicker burn, which adds to combustion stability, more motion or swirl will require less spark lead, which raises octane tolerance, handy if you want a little more compression with pump gas.

With porting & using a 1.88 inch intake ( good idea ) typical cfm would be in the 180 cfm area for the intake, these heads exhibit nice velocity which is good for a streeter.

[71SATELITE]

That is all my ride is used for Fastone. I vowed to the wife that I am going to drive my SAT until the day I can retire. In the mean time I would like to lean by trial and error about making the most of stock applications. A little massaging here and there and building good combos. Anyone can read a magazinne and bolt it on and not realy understand how and why. Thanks for all the imput fellas.

[FASTDARTCHESTER]

6-Packin

From what I have read over the years they are good for up to a 45 hp gain if prepped correctly. Check out site below...

http://cahpwww.vet.upenn.edu/~pitche...rk/sbheads.txt

Side note: I have a '69 charger with a 318 i built a few years ago. That engine used '302 heads, Hughes 1423 grind (actually Engle), M1 intake (dual plane), headers. Retained the 1.78/1.50 valves with a valve job and port work. Holley 600 on top. 3.55 rear gears...

Prior to the mods it had headers, std heads, 340 spreadbore intake with Holley 600.

My brother has an '89 Mustang with a couple of mods: Dynomax cat-back exhaust, chip, shortie headers. He could beat me pretty good prior to my mods, by about 1 1/2 cars.

After I dropped the 318 back in, we ran one night and i consistently pulled the same on him: 1 1/2 cars.

Moral: personal experience tells me the heads are good breathing heads (for a 318 because of velocity reasons). I believe this is the same head Mopar sells ported with 1.88/1.60 valves and offers the 45 hp gain.

Just my 2 cents...

[6 packin]

I agree with you! Let me clarify my opinion a little. I think the 302 heads are the best head for a street 318 for sure. The 360 head tends and will drop bottom end torque for sure. Unless the engine could wind a bit maybe above 60000 to get the best. Being the bore and stroke of a 360 will generate more torque the better heads wil not sacrifice the bottom end grunt like the 318 would. In other words if I was building a 318 for street action and even a little bit of strip I would run the 302 heads above the stock or 360 heads due to the better velocity you mentioned before which is what builds torque. As for a 360 engine I would look to better flowing heads a minumal of 200 cfm on the flow bench...................In short I agree!
Bob